Heatable medium pipes and methods for producing the same are known in the art. In particular in vehicles a number of medium pipes are provided for conveying mostly liquid media. These medium pipes tend to freeze at low temperatures, which is why they are provided with heating. Pipe connectors are used to connect at least two medium pipes or to connect a medium pipe with a given aggregate. The medium pipes often convey media which due to a relatively high freezing point tend to freeze up at ambient temperatures still at a fairly high level, which means that operability of a vehicle, for example, may be greatly impaired or even interrupted. This is true, in particular, of water pipes for windscreen washer systems, and also for medium pipes where the medium is an aqueous urea solution used as a NOx reaction additive for Diesel engines with so-called SCR catalysers.
The EP 1 985 908 A1 has disclosed a pipe connector for medium pipes, which consists of a connecting piece with connecting portion for connection with the medium pipe or an aggregate and with a transition portion adjacent to the connecting portion with current channel. At least in the area of the transition portion electrical heating means are provided in an arrangement enclosing at least partially the current channel. The electrical heating means arranged in the transition portion, i.e. outside the connecting portion, are used to prevent the respective medium from freezing within the connecting piece or to reverse the freezing process by thawing the frozen medium. The heating wire or wire strand wrapped around the outside in the manner of a coil surrounds the connecting piece, wherein at least one further coil winding is arranged inside in the area of the current channel so that when a current flows through the outer heating wire an induction is provided in the inner coil winding for generating heat. The medium pipe consists of an inner pipe line with a heat conductor arranged on the circumference, wherein pipe line and heat conductor are enclosed by an outer envelope such as by a corrugated pipe. Pipe connectors are attached at both ends of the medium pipe. Prior to fitting the corrugated pipe an adhesive tape is wrapped around the heat conductor arranged on the pipe line and thereby fixed to the pipe line. Alternatively the fixing may be effected by using a varnish or adhesive layer. The heating wires of the pipe connectors and the heat output of the pipe line are electrically interconnected, wherein the heating wire of one of the pipe connectors, respectively, is electrically switched in series with one of the winding wires of the heating wire surrounding the pipe line, and the connecting ends of the two series connections at the two pipe connectors are run to outside, where a connection to a voltage source or a further connection is provided. Alternatively it is disclosed that the heating wires of the pipe connectors and the windings surrounding the pipe line are provided in the form of a series connection of all heating wires with only one outside line connection. In each case a pipe line with heating wires wrapped around it is subsequently cut to length, before being connected with the two pipe connectors and the heating wires fitted to its outside. This is disclosed for example in the DE 10 2005 037 183 B3 or EP 1 519 098 B1. Then follows an expensive connection of the individual components which have heating wires wrapped them.
As detailed in the DE 10 2005 037 183 B3 the pipe line is initially implemented as an endless pipe and subsequently cut to a defined length. This pipe already comprises the heating wire as an electrically conductive plastic layer. As an alternative this publication of the prior art discloses that the electrical feed lines are melted into the pipe. Further it is disclosed that the pipe line may comprise grooves extending as far as the heating element and clamped or glued into the electrical feed lines. Or the electrical feed lines and, as required, further components of the pipe may be extruded, which means that the electrical feed lines and the heating element are produced together within one production process.
Correspondingly, with the electrically heatable medium pipe or liquid pipe disclosed in the EP 1 519 098 B1, the heating wire is wrapped helically around an inner plastic layer with an electrically insulating tape being wrapped directly around the plastic layer and the heating wire. The heating wire is wrapped around the plastic layer in the form of a double helix, and the ends of the heating wire are connected with a plug which can be plugged into a socket or a voltage source.
Further the EP 1 721 097 B1 discloses an electrically heatable medium pipe, where the medium pipe, a cable for heating the medium pipe and at least one electrical connector for connecting the cable to the current source are provided. The medium pipe and the cable are completely received in an outer protective envelope comprising a first tube with an inner cross-section which exceeds the outer cross-section of the medium pipe. At one end or both ends of the cabling the cable is run separate from the medium pipe and within a branch piece. It is run to a second tube on the electrical connector. The outer protective envelope encompasses the first tube, the branch piece and the second tube, wherein the branch piece is arranged between the first and second tube. This means that at least on one side the cable is not run to a pipe connector but directly into the branch line and in there to a plug connector for connection to an electrical energy source. According to this publication of the state of the art therefore, it is not the pipe connector which is heated but merely the medium pipe.
The EP 2 107 291 A2 has disclosed a fluid line, where pipe connectors are attached to the ends of an elastic pipe line. A heat conductor is fitted into the pipe line and the ends thereof are pressed in between pipe connector sections arranged in the pipe connectors. The heat conductor is connected with a connecting wire by a connecting section and thereby with an energy source. The heat conductor is laid as a loop within the pipe line and ends in the area of the loop in front of the second pipe connector. Although due to the heat conductor lying inside the pipe line the heat can be introduced directly into the medium flowing inside the medium pipe or pipe line, the wires of the heat conductor must be highly resistant against the medium flowing in the medium pipe resulting in proportionally high cost as regards the heat conductor. Further it has proven to be laborious to insert the conductor loop, i.e. the doubled-up conductor into the pipe line in a desired helical or meandering configuration. Also the costs for a pipe line of this kind are higher than for pipe lines, for which the heat conductor is run on the outside, because the inner diameter, and possibly also the wall thickness of such a pipe line, through which the heat conductor is run, must be comparatively larger in order to accommodate these without creating an obstruction in the medium flow.
It has proven to be expensive, when providing pipe connectors with heating wires wrapped around them and a pipe line separately provided with heating wire, to connect the respective heating wires of pipe connectors and pipe line, since this is time-consuming and must be carried with great care in order to ensure a proper electrical connection so that production is a drawn-out process. With the previous method a heating wire is wrapped around a pipe line, and the pipe line is pre-assembled with adhesive tape or textile adhesive tape and stored on coils. To produce the respectively required heatable medium pipe the pipe with wrapped-around heating wire must then be cut to the desired length, the adhesive tape or textile adhesive tape must be removed from both ends of the cut-to-length pipe, the respective heating wire ends must again be unwrapped, the excess pipe length must be cut off, the pipe length must be adjusted, the cuts must be cleaned and the heating wire ends must be connected with corresponding heating wire ends of heating wires arranged on pipe connectors, in particular via crimping points. On the one hand, therefore, a number of process steps is required for producing the heatable medium pipe containing the wrapped-up pipe and the pipe connectors or for initially connecting pipe and pipe connectors or the heating wires arranged on them. The provision of numerous crimping points results in high production costs. Therefore costs arise from the comparatively high production expenditure. Later, when the heatable medium pipe is installed for example in a vehicle, in particular a lorry, these crimping points are exposed to vibrations which may lead to damage to the insulation at the crimping points which may result in short-circuits and the consequences connected therewith.